There are a number of surgical procedures in which a fastener such as a screw or nail is inserted into a tissue of a patient. One surgical use involves insertion of an interference screw into a bone tunnel to secure a bone plug in place to attach an end of an anterior cruciate ligament (ACL) replacement. ACL reconstruction procedures are disclosed in U.S. Pat. Nos. 5,062,843, 4,950,270 and 4,927,421, for example.
A relatively large amount of torque must be applied to an interference screw during insertion. Similarly, insertion of nails, tacks and other fasteners can require a large insertion force.
Coatings having a low coefficient of friction have been applied to a number of surgical devices including suture needles and hypodermic needles (U.S. Pat. No. 2,814,296), and surgical staples (U.S. Pat. No. 4,655,222). Typically, most or all of the exterior surface of these devices are coated with a low coefficient of friction material such as Teflon, available from E. I. du Pont de Nemours & Co.
Other uses of a Teflon-type material include incorporation into surgical sutures (U.S. Pat. No. 4,362,162), on razor blades (U.S. Pat. No. 4,012,551), and on screws to provide self-sealing fasteners (U.S. Pat. No. 3,494,243). Other uses include application of absorbable or nonabsorbable plastics (including polytetrafluoroethylene) to staples as disclosed in U.S. Pat. No. 4,275,813. Use of Teflon and other resins for resisting corrosion has been disclosed for dental implants in U.S. Pat. No. 3,977,081 and for threaded fasteners in U.S. Pat. No. 4,835,819.
A surgical screw or other fastener which exhibits an overall coefficient of friction which is a very low may be inadvertently over-tightened or over-inserted. Problems of tendon laceration by over-inserted interference screws are described for example in L. S. Matthews et al., "Pitfalls In The Use of Interference Screws For Anterior Cruciate Ligament Reconstruction: Brief Report", J. Arthroscopic and Related Surgery 5(3):225-226 (1989). Additionally, screws which have sharp threads can nick suture and tissue during emplacement.
None of the above references discloses or suggests selectively placing a coating on a portion of a fastener to lessen required insertion force while maintaining sufficient friction to minimize over-insertion or over-penetration of the fastener.